In recent years, semiconductor devices have been developed, and a variety of semiconductor devices such as one with a silicon wafer or a glass substrate, which depends on the usage, has been manufactured.
For example, in a liquid crystal display device, a transistor and a wiring are formed over a glass substrate. An LSI, a CPU, or a memory is an aggregation of semiconductor elements each provided with an electrode which is a connection terminal, which includes a semiconductor integrated circuit (including at least a transistor and a memory) separated from a semiconductor wafer.
In the above semiconductor device, a transistor can be used for part of the components. A silicon-based semiconductor material has been known as a material for a semiconductor thin film that can be applied to a transistor. As another material, an oxide semiconductor has also attracted attention.
As a material of the oxide semiconductor, a material including zinc oxide as its component is known. In addition, a transistor which is formed using a semiconductor including zinc oxide is disclosed (Patent Documents 1 to 3).